Acoustical panels are widely used in the construction and allied industries as thermal and sound insulating media. Such panels are generally manufactured from compressed masses of wood fibers, wood pulp, cane fibers, cork granules, gypsum, rock wool, or glass fibers and combinations thereof. A preferred material is glass fibers, which may be formed into panels for use in wall or ceiling construction, sound insulating decorative roof liners for vehicles, mechanical suspension as sound absorbing and transmittance reducing media, etc. Glass fiber panels are generally manufactured by methods well known in the art, such as for example by drawing molten streams of glass into fibers and depositing the fibers in a collecting chamber where they settle, together with an applied binder, onto a traveling conveyor. The fibers form a substantially heterogeneously oriented mass of glass fibers laid in substantially stratified relationship, in planes generally parallel to the surface of the conveyor. The continuously produced fibrous mass is thereafter conveyed through compression, resin curing, and cutting stations, to form panels having overall densities from about 3 to about 12 pounds per cubic foot, depending upon their intended use. Thus, the fibrous glass panels are sufficiently porous to permit the entry of sound energy waves into the interior of the body, where the sound energy strikes individual fibers causing them to vibrate and convert the sound energy into heat energy.
U.S. Pat. No. 2,612,462 to Zettel discloses a laminated insulating block comprised of a layer of low density glass fiber aggregates and one or two surface layers of high density compressed felted glass fibers. The felted layers are compressed in a range of from one-fourth to one-sixth their original thickness, thereby producing relatively hard and dense surfaces to prevent delamination of the lower density aggregate layer The increased density surface layers of felted fibers, however, reduce the acoustical properties of the panel by retarding penetration of sound energy waves, causing a large portion of the sound energy to be reflected away from the panel.
U.S. Pat. No. 2,993,802 to Cascone discloses a fibrous acoustical panel comprised of a densified blanket of fibrous glass having a coating of particulate fibers, e.g., asbestos fibers, which increases the acoustical qualities of the panel. The blanket of fibrous glass is characterized as a mass of heterogeneously arranged fibers, containing sporadically located "swirls" or balls of glass fibers. When the surfaces of the panels are sanded smooth for the subsequent application of decorative layers, those swirls at the surfaces of the panels are truncated, thereby exposing the ends of many upstanding fibers which extend substantially perpendicularly from the surfaces. The presence of these swirls results in a lowered acoustical efficiency. The deleterious effects of these areas is overcome by the application of a dispersion of fibers in a film-forming coating liquid. The coating of fibers is claimed to result in acoustical properties better than those of the bare sanded panel of the same thickness containing the fibrous "swirls".
It would be desirable to produce a fibrous glass acoustical panel, having improved acoustical properties over the panels known in the art, especially having sound absorption capabilities for low as well as high frequency sound waves.